Topic 4 covers wave behaviour: oscillations, travelling waves, standing waves, and wave phenomena (reflection, refraction, diffraction, interference). It also covers sound waves, the EM spectrum, and polarisation.
Transverse: displacement perpendicular to propagation (light, water surface). Longitudinal: displacement parallel to propagation (sound). Wave equation: v = fλ. Amplitude (A), frequency (f), period (T = 1/f), wavelength (λ). Energy ∝ A². Wavefronts and rays represent wave propagation directions.
Reflection: angle of incidence = angle of reflection. Refraction: wave changes speed and direction at a boundary; Snell\'s law n₁sinθ₁ = n₂sinθ₂. Total internal reflection when θ > θc (sinθc = n₂/n₁, with n₁ > n₂). Diffraction: waves spread around obstacles and through gaps; maximum when gap ≈ wavelength.
Superposition: when waves overlap, displacements add. Constructive interference: path difference = nλ. Destructive: path difference = (n+½)λ. Standing waves: formed by superposition of two identical waves travelling in opposite directions. Nodes (zero displacement) and antinodes (maximum displacement). Harmonics on strings: fₙ = nv/2L.
All EM waves travel at c = 3.0 × 10⁸ m/s in vacuum. Spectrum (low to high frequency): radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays. Wavelength and frequency are inversely related: c = fλ. Polarisation: transverse waves can be polarised (oscillation restricted to one plane). Malus\'s law: I = I₀cos²θ.
Calculate the path difference (difference in distance from the two sources to the point). If the path difference equals a whole number of wavelengths (0, λ, 2λ, ...), interference is constructive (loud/bright). If it equals a half-integer number of wavelengths (λ/2, 3λ/2, ...), interference is destructive (quiet/dark). First find wavelength from v = fλ, then compare path difference to λ.
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